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Grantee Research Project Results

Grantee Research Project Results

Role of Predation in Structuring Fish Assemblages of a Species-rich Neotropical River

EPA Grant Number: U915716
Title: Role of Predation in Structuring Fish Assemblages of a Species-rich Neotropical River
Investigators: Layman, Craig A.
Institution: Texas A & M University
EPA Project Officer: Jones, Brandon
Project Period: August 1, 2000 through August 1, 2003
Project Amount: $89,494
RFA: STAR Graduate Fellowships (2000)
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems



The objective of this research project is to determine whether predators are influencing the distribution and abundance of prey fishes on sandy beaches in a species-rich tropical river. A combined experimental and food web approach is being used to analyze predator impact. Specifically, the investigator is interested in whether common prey fish of a predator guild respond to the exclusion of that guild. The main prey items of the predators will be analyzed by direct stomach content analysis, allowing experimental effects to be evaluated with regard to the known prey preferences of piscivores.


Experiments are being conducted at two scales, with the exclusion of only large predators at one scale, and the exclusion of all predators at a second. Both sets of experiments are being conducted on sandy beaches during the dry season at the Rio Cinaruco, Venezuela. This site was chosen due to its extremely high fish diversity (~260 species) and presence of numerous types of piscivores. It is believed that predators exert an important top-down influence on prey fish populations during the dry season in tropical rivers, but this has yet to be examined directly using an experimental approach.

The large scale exclusion employs 2.5 cm mesh poultry chicken wire, which serves to prevent passage of all large piscivores (e.g. peacock bass - Cichla sp., payara - Hydrolycus armatus, picua - Boulangerella sp., piranha - Serralsalmus sp.). Three experimental areas are designated and one of the three treatments randomly assigned to each area: experimental—full exclusion, control—presence of poultry wire but predator passage possible, and normal—no beach manipulation. Sampling is conducted immediately after enclosure construction and after approximately 4 weeks. The areas are sampled using a two-person seine at both day and night. The same three experimental treatments will be utilized for the complete predator exclusion. This wire mesh excludes both smaller and larger piscivore guilds effectively, allowing the response in smaller prey fishes (ones able to pass through the mesh) to be examined. These smaller areas will be sampled using a seine swept in a semicircle to completely exhaust the fauna in the experimental area.

Expected Results:

The research will directly examine and confirm the belief that predators exert an important top-down influence on prey fish populations during the dry season in tropical rivers.

Supplemental Keywords:

predation, community structure, fish, trophic cascades, top-down/bottom-up, food web, emergent impacts, diet analysis, diversity, ecology, floodplain river, tropical ecosystems, aquatic habitat, ecology, peacock bass, Cichla sp., Venezuela., RFA, Geographic Area, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, Ecosystem Protection, Aquatic Ecosystem, Ecological Effects - Environmental Exposure & Risk, Ecological Monitoring, International, Ecological Indicators, marine food web, piscivores, food web, ecosystem monitoring, tropical ecosystems, predators, fish communities, Venezuela, rivers, ecosystem indicators, predator/prey interactions, aquatic ecosystems, environmental indicators, conservation biology, biological indicators

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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